Project Summary Immune defense against bacterial infection requires activation of conserved signaling pathways that upregulate production of inflammatory mediators to clear infection. Many pathogens, including the pathogenic Yersinia inhibit these signaling pathways in order to evade host immune defenses. Yersinia pseudotuberculosis (Yp) blocks NF-?B and MAPK signaling and interferes with inflammatory gene expression but also induces apoptosis in innate immune cells. We recently demonstrated that YopJ-induced apoptosis itself is critical for host defense against Yp infection. How apoptosis contributes to immune defense against pathogens that block immune signaling pathways, and how this apoptosis is regulated remains poorly understood. We have identified a novel regulator of apoptosis pathways, termed CARD19, which plays a key role in multiple pathways of caspase-dependent cell death. Notably, CARD19 deficiency results in increased susceptibility to oral infection by Y. pseudotuberculosis further supporting the role of cell death in response to Yersinia infection as a key host immune protective mechanism. Our preliminary data demonstrate that CARD19 is localized to the mitochondria, similarly to another mitochondrial CARD-containing protein, MAVS. Our central hypothesis is that Yersinia infection promotes cell death via oligomerization of CARD19 and disruption of mitochondrial function. Moreover, we hypothesize that this cell death releases pro-inflammatory signals that alert uninfected neighboring cells to the presence of infection. How CARD19-induced cell death is coupled to inflammatory responses and host defense against bacterial infection is not known. This pathway likely responds to many pathogens that block critical innate immune signaling pathways and in the context of pathological stimuli that lead to CARD19-induced cell death. We propose two Specific Aims to address this important gap in our knowledge. First we will define the molecular basis for CARD19-induced cell death. Second, we will determine the contribution of CARD19 to downstream pathogen-specific immune responses and will dissect whether CARD19 functions in a cell extrinsic manner via release of specific alarmins to mediate host immune defense.